This question tests the knowledge of common inorganic compounds and their existence/stability, particularly focusing on the oxidation states and bonding capabilities of elements.

The existence of a compound depends on various factors, including the stability of the oxidation states of its constituent elements and the feasibility of forming the required bonds. Chromium typically forms stable compounds in +3 and +6 oxidation states. Halogens like Cl and Br can act as ligands or form covalent bonds.

Chromyl halides are compounds of chromium in its +6 oxidation state. Chromyl chloride, ${\mathrm{CrO}}_2{\mathrm{Cl}}_2$, is a well-known stable compound. However, chromyl bromide, ${\mathrm{CrO}}_2{\mathrm{Br}}_2$, does not exist. This is because bromine is a weaker oxidizing agent than chlorine, and the ${\mathrm{Cr}}^{6+}$ ion is a strong oxidizing agent. The combination of ${\mathrm{Cr}}^{6+}$ with bromide ions leads to the oxidation of bromide to bromine and reduction of ${\mathrm{Cr}}^{6+}$ to a lower oxidation state (typically ${\mathrm{Cr}}^{3+}$), making ${\mathrm{CrO}}_2{\mathrm{Br}}_2$ unstable and non-existent under normal conditions.

• A) ${\mathrm{CrO}}_2{\mathrm{Br}}_2$: This compound does not exist due to the strong oxidizing nature of ${\mathrm{Cr}}^{6+}$ and the reducing nature of ${\mathrm{Br}}^{-}$ ions, leading to redox reactions rather than stable compound formation.
• B) ${\mathrm{CrO}}_2{\mathrm{Cl}}_2$: Chromyl chloride is a stable, well-known compound used in the chromyl chloride test for chlorides. Chromium is in the +6 oxidation state.
• C) ${\mathrm{POCl}}_3$: Phosphorus oxychloride is a stable, common inorganic compound used as a reagent in organic synthesis. Phosphorus is in the +5 oxidation state.
• D) $\mathrm{BiOCl}$: Bismuth oxychloride is a stable compound, often used in cosmetics. Bismuth is in the +3 oxidation state.

Correct Answer: (A)